Life history and exploitation.pdf (1.884Mb)

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Herring

S e c t i o n I: L i f e h i s t o r y .

LIFE HISTORY AND EXPLOITATION OF THE NORWEGIAN SPRING SPAWNING HERRING

Johs. Hamre

I n s t i t u t e of Marine Research P.O. Box 1870 Nordnes N-5024 Bergen, Norway

ABSTRACT

T h i s paper i s a review of t h e h i s t o r y and e x p l o i t a t i o n of t h e Norwegian s p r i n g spawning h e r r i n g s t o c k . I n a v i r g i n s t a t e t h e biomass of t h i s s t o c k may have ranged from

15

t o 20 m i l l i o n tonnes and i t was t h e most important f i s h r e s o u r c e i n t h e Northeast A t l a n t i c . The a d u l t s t o c k u t i l i z e d t h e r i c h plankton production along t h e P o l a r Front i n t h e Norwegian Sea b u t spawned d u r i n g w i n t e r on t h e Norwegian w e s t c o a s t . These spawners formed t h e b a s i s f o r t h e l a r g e s t f i s h e r y i n Europe f o r c e n t u r i e s . The young and adolescent h e r r i n g a r e d i s t r i b u t e d i n Norwegian c o a s t a l w a t e r s and i n t h e Barents Sea where they c o n s t i t u t e t h e most important prey s p e c i e s f o r many s t o c k s of p r e d a t o r s , both of f i s h , b i r d s and mammals.

Due t o t e c h n i c a l advances t h e e x p l o i t a t i o n of t h e h e r r i n g i n c r e a s e d tremendously i n t h e 1960's and t h e a d u l t s t o c k was f i s h e d o u t completely i n 1970. Some small components of j u v e n i l e h e r r i n g d i d however s u r v i v e , and spawned on t h e t r a d i t i o n a l spawning grounds i n 1973. A f t e r spawning t h e h e r r i n g d i d n o t m i g r a t e t o t h e t r a d i t i o n a l f e e d i n g a r e a i n t h e Norwegian Sea, b u t remained i n Norwegian c o a s t a l w a t e r s throughout t h e y e a r . I n l a t e r y e a r s t h e s t o c k has recovered s l o w l y , b u t t h e o l d t r a d i t i o n a l migration p a t t e r n of h e r r i n g between t h e P o l a r Front a r e a and t h e Norwegian c o a s t h a s n o t y e t been r e t a i n e d . It i s concluded t h a t t h e break down of t h e l i f e c y c l e s of t h e h e r r i n g i s t h e prime reason f o r t h e r e c e n t c r i s i s which h a s developed i n t h e Barents Sea s t o c k s and f i s h e r i e s .

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L i f e h i s t o r y and e x p l o i t a t i o n

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INTRODUCTION

The p r e s e n t paper reviews t h e h i s t o r y of t h e f i s h e r y and r e s e a r c h on t h e Norwegian s p r i n g spawning h e r r i n g and t h e r e g u l a t i o n measures i n t r o d u c e d t o conserve t h e s t o c k i n r e c e n t y e a r s . I n conclusion emphasis i s l a i d on t h e importance of t h e s t o c k f o r t h e balance i n t h e p r e d a t i o n / p r e y r e l a t i o n s h i p i n t h e ecosystem of t h e Norwegian Sea and Barents Sea.

STOCK IDENTITY

The term "Atlanto-Scandian h e r r i n g " was introduced by Johansen

(1919)

and i s used a s a common name f o r t h r e e s t o c k s : Norwegian s p r i n g spawners, I c e l a n d i c s p r i n g spawners, and I c e l a n d i c summer spawners.

The Norwegian s p r i n g spawners a r e t h e l a r g e s t of t h e s e s t o c k s , w i t h spawning grounds s i t u a t e d mainly along t h e Norwegian c o a s t . STOCK STRUCTURE

Whether t h e Norwegian spring-spawning h e r r i n g c o n s t i t u t e a s i n g l e homogeneous s t o c k has been t h e s u b j e c t of c o n f l i c t i n g s c i e n t i f i c views. Broch (1908) found t h a t t h e v e r t e b r a l counts o f t h e spawners were n o t t h e same throughout t h e t o t a l d i s t r i b u t i o n range. Lea (1929) observed t h a t t h e s c a l e s of young h e r r i n g from n o r t h e r n and s o u t h e r n Norway d i f f e r e d i n t h e p a t t e r n of t h e i r w i n t e r r i n g s , r e f l e c t i n g d i f f e r e n c e s i n t h e i r growth r a t e s d u r i n g adolescence. I n t h e l i g h t of such d i f f e r e n c e s , Schnackenbeck (1931) concluded t h a t t h e Norwegian spawning p o p u l a t i o n was d i v i s i b l e i n t o a t l e a s t two " r a c e s " , and O t t e s t a d (1934) s p l i t t e d t h e s t o c k i n t o a n o r t h e r n and a s o u t h e r n component with spawning grounds t o t h e n o r t h and s o u t h of More r e s p e c t i v e l y . RunnstrØm (1937,1941), on t h e o t h e r hand, claimed t h a t such a s t r i c t s e p a r a t i o n was n o t c o n s i s t e n t with t h e a v a i l a b l e evidences.

Østvedt (1958) found t h a t t h e r e was an i n c r e a s i n g i n t e r m i x i n g of t h e two t y p e s with age, and t h a t t h e p r o p o r t i o n s of t h e two t y p e s v a r i e d c o n s i d e r a b l y between y e a r c l a s s e s . H e concluded t h a t h e r r i n g of t h e two growth t y p e s could n o t be members of d i f f e r e n t " r a c e s " . The r e s u l t s of t h e tagging experiments c a r r i e d o u t on t h e Norwegian spawning grounds and i n t h e oceanic f e e d i n g a r e a s (Dragesund and Jakobsson, 1963) a l s o show t h a t t h e spawners change t h e i r grounds from y e a r t o y e a r along t h e Norwegian c o a s t . I n l i g h t of a l l t h e a v a i l a b l e evidences i t i s t h e r e f o r e reasonable t o assume t h a t t h e Norwegian s p r i n g spawners a r e members of a s i n g l e s t o c k and t h a t t h e two d i s t i n c t i v e growth types a r e h e r r i n g which o r i g i n a t e from d i f f e r e n t n u r s e r y a r e a s .

DISTRIBUTION AND MIGRATION 1. Adult h e r r i n g

Knowledge of t h e d i s t r i b u t i o n and migration of t h e a d u l t h e r r i n g i s obtained from s e v e r a l s o u r c e s , such a s r a c i a l a n a l y s i s ( F r i d r i k s s o n , 1 9 6 3 ) , t a g g i n g experiments ( F r i d r i k s s o n and Aasen, 1952; Jakobsson, 1963) and a c o u s t i c surveys (Devold, 1963 ; Anon.

,

1964 ; and Jakobsson,

1971).

For many y e a r s t h e s e surveys were c a r r i e d o u t j o i n t l y by Denmark, I c e l a n d , Norway and t h e USSR.

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l L i f e k i s t o r y and e x p l o i t a t i o n .

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2. H e r r i n g p e r i o d s

For c e n t u r i e s t h i s h e r r i n g has been t h e b a s i s f o r one o f t h e l a r g e s t f i s h e r i e s i n Norway, and f o r more than 100 y e a r s t h e s u b j e c t of s c i e n t i f i c i n v e s t i g a t i o n s . I n

1857

t h e Norwegian Government gave Dr.Axel Boeck

(1871)

t h e t a s k of i n v e s t i g a t i n g t h e s o - c a l l e d " s p r i n g h e r r i n g " . Boeck brought t o g e t h e r many h i s t o r i c a l f a c t s about t h e Norwegian s p r i n g h e r r i n g f i s h e r y and he found t h a t t h e f i s h e r y had p e r i o d s of high abundance a l t e r n a t i n g w i t h p e r i o d s of extreme s c a r c i t y . According t o Boeck, t h e symptoms of a Norwegian h e r r i n g p e r i o d approaching i t s end a r e t h a t t h e h e r r i n g a r r i v e l a t e r each y e a r a t t h e Norwegian c o a s t , which had been t h e s i t u a t i o n i n t h e 1870's.

Boeck found s i m i l a r p e r i o d i c i t y i n t h e h e r r i n g f i s h e r y o f Bohuslan i n Sweden and suggested t h a t t h i s f i s h e r y could o r i g i n a t e from t h e Norwegian s p r i n g spawning h e r r i n g s t o c k . Boeck's view t h a t t h e s p r i n g h e r r i n g could l e a v e t h e u s u a l spawning grounds c r e a t e d g r e a t f e a r among t h e fishermen, and t h e Norwegian Government asked G.O. S a r s t o i n v e s t i g a t e t h i s problem.

A f t e r t h r e e y e a r s of i n v e s t i g a t i o n G.O.Sars succeeded i n drawing a f a i r l y c o r r e c t p i c t u r e of t h e l i f e h i s t o r y o f t h e Norwegian h e r r i n g . He b e l i e v e d t h a t t h e " s p r i n g h e r r i n g " l i v e d i n t h e s u r f a c e l a y e r s of t h e open s e a between S c o t l a n d , Norway and I c e l a n d , f e e d i n g on copepods, and a t t a i n i n g m a t u r i t y when b e i n g about 6 y e a r s o l d . The spawning a r e a was l o c a t e d o f f t h e Norwegian c o a s t between Stavanger and K r i s t i a n s u n d , from which t h e l a r v a e were s p r e a d northwards by t h e c u r r e n t s . I n t h e y e a r s 1868-1874 g r e a t q u a n t i t i e s of s o - c a l l e d " l a r g e h e r r i n g " were caught o f f n o r t h e r n Norway i n t h e autumn. O r i g i n a l l y he regarded t h e " l a r g e h e r r i n g " a s a s p e c i a l t r i b e w i t h unknown spawning grounds b u t l a t e r he found t h a t t h e connection between t h e " s p r i n g h e r r i n g " and " l a r g e h e r r i n g " f i s h e r i e s was c l o s e r t h a n he e a r l i e r b e l i e v e d . With r e s p e c t t o a l t e r n a t i n g h e r r i n g p e r i o d s , G.O. S a r s views were d i f f e r e d from t h o s e of Boeck. S a r s had found j u v e n i l e h e r r i n g f u r t h e r o f f t h e c o a s t than was u s u a l and considered i t l i k e l y t h a t t h e h e r r i n g would soon r e t u r n t o t h e o l d spawning grounds. H e q u e s t i o n e d whether h e r r i n g p e r i o d s r e a l l y d i d e x i s t i n t h e Norwegian h e r r i n g f i s h e r i e s and thought i t u n l i k e l y t h a t t h e r e should be any connection between t h e " s p r i n g h e r r i n g " and t h e h e r r i n g r e s p o n s i b l e f o r t h e g r e a t h e r r i n g f i s h e r i e s i n Bohuslan.

Jensen

(1881)

and Buck

(1888)

continued t h e h e r r i n g s t u d i e s i n t h e f o l l o w i n g y e a r s and d e s c r i b e d t h e h e r r i n g on t h e w e s t c o a s t as "new h e r r i n g " c o n s i s t i n g of a mixture of immature and mature h e r r i n g which i n s i z e became s i m i l a r t o t h e s p r i n g h e r r i n g . The h e r r i n g spawned on t h e u s u a l spawning grounds b u t was f a r less abundant a s b e f o r e 1870.

The mature h e r r i n g found i n shallow a r e a s o f f n o r t h e r n Norway i n 1868-

1874

were i n v e s t i g a t e d by Boeck and S a r s and were d e s c r i b e d a s h e r r i n g of t h e same s i z e a s t h e " s p r i n g h e r r i n g " , b u t i n much b e t t e r c o n d i t i o n . The o v a r i e s showed t h a t they were n o t ready t o spawn. I n December, t h e " l a r g e h e r r i n g " disappeared from n o r t h e r n Norway b u t t h e i r spawning ground was never observed.

During t h e w i n t e r o f

1877,

g r e a t s c h o o l s o f h e r r i n g were discovered p e n e t r a t i n g t h e Bohuslan s k e r r i e s , and f o r 20 w i n t e r s i n s u c c e s s i o n , a g r e a t h e r r i n g f i s h e r y was c a r r i e d o u t t h e r e . The h e r r i n g had been a b s e n t s i n c e 1808, b u t s i m i l a r f i s h i n g p e r i o d s i n t h i s a r e a a r e t r a c e d back i n h i s t o r y f o r about 1000 y e a r s , and i t l o o k s a s i f t h e Bohuslan and Norwegian " s p r i n g h e r r i n g " f i s h i n g p e r i o d s occured a l t e r n a t e l y . A t t h e time of t h e Bohuslan f i s h e r y , h e r r i n g f i s h e r i e s als0 grew up on

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t h e Norwegian s i d e of t h e border t o Sweden (Ljungman, 1882; 0 . P e t t e r s s o n , 1922; Devold 1963)

.

During t h e w i n t e r of 1895-96 Norwegian fishermen caught g r e a t q u a n t i t i e s of l a r g e h e r r i n g i n t h e Skagerak f o r t h e l a s t t i m e . It was a l s o t h e l a s t w i n t e r i n which g r e a t h e r r i n g f i s h e r i e s o c c u r r e d i n s i d e t h e s k e r r i e s i n Bohuslan. The f o l l o w i n g w i n t e r h e r r i n g c o n c e n t r a t i o n s along t h e c o a s t of western Norway were of t h e same magnitude a s i n t h e good f i s h i n g w i n t e r s b e f o r e 1870 (Buvik, 1895-99)#

I n t h e autumn of 1896 onwards, g r e a t s c h o o l s of h e r r i n g were d i s c o v e r e d o f f Møre. They were c a l l e d " l a r g e h e r r i n g " , and an e x t e n s i v e h e r r i n g f i s h e r y began on them. These h e r r i n g s c h o o l s disappeared b e f o r e Christmas, b u t i n January new s c h o o l s a r r i v e d and moved southwards a l o n g t h e c o a s t and were l a t e r caught from Haugesund southwards t o Lindesnes. These s c h o o l s were c a l l e d " s p r i n g h e r r i n g " . I n t h e beginning of t h i s c e n t u r y t h e h e r r i n g f i s h e r i e s had two s e a s o n s , one based on t h e " l a r g e h e r r i n g " , t h e o t h e r on t h e " s p r i n g h e r r i n g " . The l a r g e h e r r i n g a r r i v e d each y e a r l a t e r i n t h e c o a s t a l w a t e r s and a f t e r 1921 no h e r r i n g a r r i v e d i n t h e Møre r e g i o n b e f o r e t h e 1st o f January. I n t h e 1 9 3 0 ' s t h e h e r r i n g spawned i n e a r l y February, whereas t h e spawning i n t h e 1 9 5 0 ' s took p l a c e i n e a r l y March.

Simultaneously t h e d i s t r i b u t i o n a r e a decreased and t h e c e n t e r of spawning moved northwards. The spawning grounds s o u t h o f Bergen were abandoned i n t h e l a t e

l95O1s,

and i n l a t e r y e a r s t h e spawning h a s been c o n c e n t r a t e d on t h e c o a s t from M@re t o Lofoten (Devold, 1963).

The simultaneous changes i n t h e spawning time and i n t h e displacement of t h e spawning grounds northwards gave rise t o a renewed d i s c u s s i o n of a l t e r n a t i n g h e r r i n g p e r i o d s between t h e r i c h Bohuslan f i s h e r y and t h e w i n t e r h e r r i n g f i s h e r y on t h e Norwegian west c o a s t . I n a s e r i e s of a r t i c l e s and p u b l i c a t i o n s i n t h e 1 9 5 0 ' s Finn Devold supported t h e theory o f a l t e r n a t i n g h e r r i n g p e r i o d s and p r e d i c t e d t h a t t h e displacement of t h e spawning grounds and t h e d e l a y i n t h e spawning t i m e i n d i c a t e d t h e end of t h e h e r r i n g f i s h e r y on t h e Norwegian w e s t c o a s t (Devold 1950,1955,1959,1960,1963,1964). Devold a l s 0 developed an h y p o t h e s i s which e x p l a i n e d t h e p r o c e s s e s which governed t h e r e l a t i o n between t h e spawning behaviour and t h e m i g r a t i o n . H i s b a s i c assumption was t h a t i t t a k e s a l i t t l e more t h a n one y e a r between s u c c e s s i v e spawnings. The h e r r i n g w i l l then a r r i v e a t t h e Norwegian c o a s t l a t e r each y e a r and a l s o l e a v e t h e c o a s t l a t e r . When p o s t spawners a r e l e a v i n g l a t e , t h e y have t o p a s s t h e a r e a on t h e Norwegian c o n t i n e n t a l s h e l f a f t e r t h e copepods have e n t e r e d s u r f a c e l a y e r s , i n A p r i l . The h e r r i n g w i l l t h e r e f o r e s t a r t f e e d i n g h e r e and w i l l move northwards o f f t h e Norwegian c o a s t .

I n t h e autumn, t h e h e r r i n g used t o m i g r a t e t o t h e c o l d a r c t i c water i n t h e E a s t I c e l a n d i c C u r r e n t f o r w i n t e r i n g . Being o f f n o r t h e r n Norway they w i l l be f a r from t h e a r c t i c water of t h e E a s t I c e l a n d i c C u r r e n t . Cold w a t e r w i l l , however, be a v a i l a b l e n e a r t h e Norwegian c o a s t , where t h e w i n t e r c o o l i n g of t h e c o a s t a l w a t e r s w i l l have s t a r t e d , and t h e s e w a t e r s w i l l t h e r e f o r e b e invaded f o r w i n t e r i n g . S i n c e t h e temperature of t h e c o a s t a l water of n o r t h e r n Norway is h i g h e r t h a n t h a t of t h e E a s t I c e l a n d i c C u r r e n t , t h e gonads of t h e s e h e r r i n g w i l l develop f a s t e r and spawning w i l l t a k e p l a c e e a r l i e r than i n t h e preceding season. A f t e r spawning t h e s e h e r r i n g w i l l l e a v e t h e Norwegian c o a s t e a r l y , and r e t u r n f o r f e e d i n g along t h e P o l a r Front e a r l i e r than u s u a l . The n e x t autumn t h e i r spawning m i g r a t i o n w i l l t h e r e f o r e s t a r t e a r l y . , and t h e m i g r a t i n g s c h o o l s w i l l have t o p a s s through water masses of a h i g h e r temperature than u s u a l . The Norwegian c o a s t a l

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LIFE HISTORY

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L i f e h i s t o r y aiid e x p l o i t a t i o n

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w a t e r s o f f More, where t h e h e r r i n g u s u a l l y a r r i v e , have a s u r f a c e temperature above 10 C i n t h e autumn. The h e r r i n g w i l l avoid t h i s warm o water and move toward t h e B a l t i c water of a temperature of s i x t o seven degrees. The h e r r i n g may then pass through t h e Norwegian Channel i n t o t h e Skagerak, and spawn o f f t h e Norwegian s o u t h c o a s t , and o f f Bohuslan. A f t e r spawning t h e h e r r i n g invade t h e c o a s t a l a r e a s of Bohuslan, and t h e s o u t h - e a s t c o a s t of Norway where t h e y spend t h e

" r e s t i n g t i m e " i n c o l d water. The delay i n spawning t i m e by y e a r s w i l l however i n c r e a s e t h e chances t h a t t h e h e r r i n g meet c o l d B a l t i c water i n t h e Skagerak on t h e spawning migration. I f t h e B a l t i c water is t o o c o l d , t h e h e r r i n g w i l l f i n d warmer spawning grounds f u r t h e r west. I f t h e h e r r i n g have t o l e a v e a spawning ground and f i n d a new one, they w i l l r e t u r n t o t h i s new ground f o r t h e succeeding spawnings. I n t h i s way t h e h e r r i n g a r e d r i v e n o u t of t h e Skagerak, and l a t e r a l s o have t o avoid t h e s o u t h e r n spawning grounds i n western Norway. I n t h i s way r i c h h e r r i n g p e r i o d s of t h e Bohuslan and of t h e Norwegian w e s t c o a s t may a l t e r n a t e and t h e hypothesis a l s o e x p l a i n e t h e i n t e r m e d i a t e occurrence of t h e " l a r g e h e r r i n g " w i n t e r i n g i n t h e n o r t h Norwegian f j o r d s .

Devolds h y p o t h e s i s was s t r o n g l y opposed by Swedish s c i e n t i s t s (Andersson 1950, 1956, Hoglund 1959,1960,1977). Based on s i z e and age composition a n a l y s i s of t h e Bohuslan h e r r i n g , t h e y claimed t h a t t h i s s t o c k had no connections with t h e Norwegian s p r i n g spawning h e r r i n g , b u t was r e l a t e d t o t r i b e s which were u s u s a l l y f i s h e d i n t h e North Sea, Skagerak and K a t t e g a t .

The Norwegian west c o a s t h e r r i n g f i s h e r y c o l l a p s e d i n t h e 1960's due t o d e p l e t i o n of t h e s t o c k by t h e f i s h e r y . The f e e d i n g migration t o t h e P o l a r Front a r e a was i n t e r r u p t e d i n t h e e a r l y 1 9 7 0 ' s . and i n t h e subsequent y e a r s t h e postspawners have been f e e d i n g o f f t h e Norwegian c o a s t and have wintered i n t h e Norwegian f j o r d s a s presupposed by Devold's h y p o t h e s i s . The maturing o f t h e h e r r i n g h a s , however, n o t developed a s p r e d i c t e d . The h e r r i n g have matured i n February-March a s they d i d i n t h e 1960's and have spawned on t h e t r a d i t i o n a l spawning grounds from More t o Lofoten. I n 1989 a s m a l l component a l s o spawned , on t h e southern grounds f o r t h e f i r s t t i m e s i n c e 1959, and t h i s spawning took p l a c e r a t h e r l a t e i n t h e spawning season ( f i r s t h a l f of March)

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3.

Migration p a t t e r n

The migration o f t h e a d u l t h e r r i n g s t o c k i s recorded i n d e t a i l s i n c e t h e e a r l y 1950's. A f t e r spawning most of t h e s p e n t h e r r i n g moved l northwestwards i n t o t h e Norwegian Sea where they f e d on zooplankton.

The l a r g e r f i s h reached t h e P o l a r Front i n June and J u l y and some

l

l c r o s s e d i n t o t h e c o l d water. The l i m i t of t h e summer f e e d i n g migration extended from t h e Spitsbergen-Jan Mayen a r e a i n t h e n o r t h t o t h e western borders of t h e E a s t I c e l a n d i c Current i n t h e s o u t h . The l a r g e r f i s h moved f u r t h e r t o t h e northwest than t h e s m a l l e r f i s h (Marty, 1959; Marty and Wilson, 1960).

During t h e autumn t h e h e r r i n g was found i n t h e southwestern p a r t of t h e Norwegian Sea along t h e borders of t h e E a s t I c e l a n d i c Current. The r i p e n i n g h e r r i n g wintered i n an a r e a o f f East I c e l a n d . I n December and January prespawning c o n c e n t r a t i o n s moved towards t h e Norwegian c o a s t . Devold (1951,1959,1963) d e s c r i b e d i n d e t a i l t h e spawning migration towards t h e c o a s t i n t h e 5 0 ' s . H e found t h a t t h e h e r r i n g g a t h e r i n cold-water pockets b e f o r e p e n e t r a t i n g t h e warm A t l a n t i c Current i n t o t h e c o l d e r Norwegian c o a s t a l water. The h e r r i n g u s u a l l y a r r i v e a t ^{t h e}

(6)

...

Norwegian c o a s t o f f Mare and spread f a r t h e r s o u t h and n o r t h t o spawn.

T h i s d e s c r i p t i o n of t h e d i s t r i b u t i o n and migratory p a t t e r n of t h e a d u l t s t o c k r e f e r s t o a s t a t e when t h e s t o c k was a t a r e l a t i v e l y h i g h l e v e l . Between l950 and 1962 t h e s t o c k d e c l i n e d . The spawning was g r a d u a l l y d i s p l a c e d northwards, and a f t e r 1959 spawning s o u t h of Bergen was n e g l i g i b l e (Devold, 1963; Dragesund, 1970)

.

I n 1950-1962 t h e main summer f e e d i n g grounds v a r i e d somewhat b u t remained i n t h e Iceland-Jan Mayen a r e a , b u t i n 1963-1966 a s t o c k component f e d and wintered i n an a r e a s o u t h of BjØrnøya ( F i g l ) The d e n s e s t summer c o n c e n t r a t i o n s were u s u a l l y found n e a r t h e b o r d e r s of t h e E a s t I c e l a n d i c C u r r e n t . I n t h e autumn t h e h e r r i n g assembled on t h e w i n t e r i n g grounds s i t u a t e d n e a r t h e s o u t h e r n and southwestern b o r d e r s of t h e E a s t I c e l a n d i c Current.

Jan H a y e p

---r Feeding migratio

20' 10' O'

Fig. 1 Migration of Norwegian s p r i n g spawning h e r r i n g p r i o r t o 1970.

4.

Migration p a t t e r n a f t e r 1970

The summer and autumn f i s h e r y f o r a d u l t h e r r i n g terminated i n 1969, and s i n c e then no h e r r i n g have been recorded i n t h e P o l a r F r o n t a r e a of t h e Norwegian Sea. The w i n t e r h e r r i n g f i s h e r y on t h e spawning grounds decreased s h a r p l y a f t e r i967 b u t continued on t h e d e p l e t e d s t o c k u n t i l

1971.

The s t o c k of immature h e r r i n g was almost d e p l e t e d i n 1969, and immature f i s h recorded i n t h e e a r l y 1 9 7 0 ' s belonged mainly t o t h e 1969 y e a r c l a s s .

The u s e of h e r r i n g f o r r e d u c t i o n purposes was p r o h i b i t e d i n Norway from January

1971.

T h i s r e g u l a t i o n probably prevented t h e complete e x t i n c t i o n of t h e 1969 y e a r c l a s s . Purse s e i n e r s f i s h i n g f o r c a p e l i n r e p o r t e d c o n c e n t r a t i o n s of young h e r r i n g o f f t h e c o a s t of Finnmark d u r i n g t h e w i n t e r of 1971, and s e v e r a l c a t c h e s of f a t h e r r i n g were r e l e a s e d t h a t y e a r because of t h e ban on t h e i n d u s t r i a l f i s h e r y . T h i s

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LIFE HISTORY

-

h e r r i n g

...

l a s t remnant of t h e s t o c k probably survived a s j u v e n i l e s somewhere i n t h e Barents Sea o r i n t h e n o r t h e a s t e r n p a r t of t h e Norwegian Sea.

I n 1972, f i v e p u r s e s e i n e r s w e r e c h a r t e r e d t o survey t h e spawning grounds. P r a c t i c a l l y no spawning h e r r i n g were recorded (Dragesund, B j e r k e , and S a n g o l t , 1972). The absence o f spawning h e r r i n g and h e r r i n g l a r v a e i n 1972 and t h e very low abundance o f t h e 1970-1972 y e a r c l a s s e s i n t h e spawning s t o c k demonstrates t h a t t h e a d u l t s t o c k of Norwegian spring-spawning h e r r i n g c o l l a p s e d i n t h e e a r l y 1970's.

I n November 1972 s h o a l s of maturing h e r r i n g were recorded o f f western Finnmark ( i n t h e Ingøy Deep), and i n January 1973 a Norwegian p u r s e s e i n e r l o c a t e d h e r r i n g s h o a l s some 50 nm northwest of Ingøy. Most of t h e s e h e r r i n g belonged t o t h e 1969 y e a r c l a s s , and were obviously on t h e i r way t o t h e c o a s t t o spawn. Maturing h e r r i n g o f t h e 1969 y e a r c l a s s were found, l a t e r i n 1973, o f f V e s t e r å l e n and Lofoten. These h e r r i n g probably spawned i n t h e Lofoten a r e a i n March, because h e r r i n g l a r v a e were found t h e r e i n A p r i l . The t r a d i t i o n a l spawning grounds o f f Mgre and Trgndelag were surveyed throughout t h e spawning season i n

1973.

No c o n c e n t r a t i o n of spawning h e r r i n g was found, b u t g i l l - n e t c a t c h e s of h e r r i n g with running gonads i n d i c a t e d t h a t some spawning took p l a c e . This was l a t e r confirmed by t h e l a r v a l survey t h a t y e a r . The spawning s t o c k o f f Møre was a l c o dominated by t h e 1969 y e a r c l a s s

(Dragesund, Bjerke, and S a n g o l t ,

1973).

Two components of immature h e r r i n g survived t h e heavy e x p l o i t a t i o n i n t h e 1 9 6 o t s , one i n t h e Barents Sea and t h e o t h e r on t h e west c o a s t of Norway. Both components spawned f o r t h e f i r s t time i n 1973, one o f f t h e Mgre c o a s t , t h e o t h e r o f f Lofoten. According t o r e c o r d i n g s of maturing h e r r i n g i n 1973, t h e n o r t h e r n component was by f a r t h e l a r g e r . A f t e r spawning, t h e h e r r i n g d i d n o t l e a v e t h e c o a s t a s i n p r e v i o u s y e a r s , b u t migrated i n t o i n s h o r e w a t e r s t o f e e d d u r i n g summer and autumn. No spawning was observed o f f Lofoten i n t h e w i n t e r of 1974. The n o r t h e r n component migrated southward, and s i n c e

1974

spawning h a s taken p l a c e on t h e t r a d i t i o n a l spawning grounds o f f Møre and Trgndelag (Dragesund e t . a l 1980).

The t r a d i t i o n a l migration p a t t e r n of t h e h e r r i n g was t h u s i n t e r r u p t e d i n t h e e a r l y 7 0 ' s and h a s n o t y e t been r e t a i n e d . The two s t o c k components have developed a s s e p a r a t e u n i t s , with d i f f e r e n t spawning grounds, f e e d i n g a r e a s and w i n t e r i n g l o c a l i t i e s ( F i g u r e

3 ) .

The s o u t h e r n component has\spawned on t h e s o u t h e r n c o a s t o f f Møre and some y e a r s a l s 0 f u r t h e r s o u t h . A s a l r e a d y mentioned, s h o a l s of spawning h e r r i n g were i n

1989

recorded on t h e s o u t h e r n spawning grounds i n t h e beginning of March. These grounds have been abandoned by t h e h e r r i n g s i n c e t h e l a t e 1950's. The s o u t h e r n component has f e d d u r i n g summer and autumn o f f t h e c o a s t of Møre and Trøndelag, and wintered i n t h e f j o r d s of n o r t h e r n Møre. The s o u t h e r n component has u s u a l l y l e f t t h e w i n t e r i n g a r e a i n l a t e January and a r r i v e d a t t h e spawning ground i n t h e e a r l y February. Growth r a t e , r e c r u i t m e n t and age s t r u c t u r e of t h e h e r r i n g i n d i c a t e t h a t t h i s s t o c k component has developed a s a s e p a r a t e u n i t . This i s a l s 0 supported by t h e recovery of tagged h e r r i n g . The s o u t h e r n component of s p r i n g spawners has t o some e x t e n t been mixed with autumn spawners and h e r r i n g from l o c a l s t o c k s which spawn i n t h e f j o r d s .

The n o r t h e r n component has spawned i n t h e a r e a from n o r t h e r n Møre (Buagrunnen) t o Lofoten. This h e r r i n g has spawned some weeks l a t e r t h a n t h e h e r r i n g of t h e s o u t h e r n component. The n o r t h e r n component has

(8)

...

a l c o f e d on t h e Norwegian s h e l f d u r i n g summer and autumn, b u t more o f f s h o r e and f a r t h e r n o r t h . The s h o a l s have moved northwards d u r i n g t h e summer and have u s u a l l y been found o f f Lofoten i n t h e e a r l y autumn. I n September t h e y have migrated i n t o t h e V e s t f j o r d e n a r e a and wintered i n t h e f j o r d s o f Lofoten and V e s t e r å l e n . The h e r r i n g have r e t u r n e d t o t h e same f j o r d s every y e a r b u t when t h e abundant B a r e n t s Sea component of t h e

1983

y e a r c l a s s migrated t o t h e c o a s t a l a r e a f o r w i n t e r i n g i n t h e autumn 1986, t h e w i n t e r i n g a r e a was expanded t o i n c l u d e s e v e r a l new f j o r d s i n t h e same r e g i o n .

I n t h e y e a r s 1988 and

89

most of t h e 1983 y e a r c l a s s wintered i n t h e i n n e r p a r t of V e s t f j o r d e n . When t h e 1983 y e a r c l a s s r e c r u i t e d t o t h e spawning s t o c k t h e s e p a r a t i o n of t h e h e r r i n g i n two d i f f e r e n t s t o c k u n i t s disappeared. Tag r e t u r n s from t h e w i n t e r f i s h e r y i n 1989 do, h o w e v e r , i n d i c a t e t h a t t h e Barents Sea component of t h e

1983

y e a r c l a s s h a s invaded a l l spawning grounds on More, whereas t h e h e r r i n g from t h e More-Trondelag a r e a a r e d i s p l a c e d t o spawning grounds f a r t h e r t o t h e

s o u t h ( F i g .

3 B ) .

5.

D i s t r i b u t i o n of young and a d o l e s c e n t h e r r i n g

U n t i l t h e beginning of t h e 1 9 6 0 ' s l i t t l e was known about t h e d i s t r i b u t i o n and m i g r a t i o n of t h e e a r l y s t a g e s of Norwegian s p r i n g spawners. Devold (1950) showed t h a t O-group h e r r i n g of t h e r i c h 1950 y e a r c l a s s were d i s t r i b u t e d f a r o f f s h o r e i n t h e n o r t h e a s t e r n p a r t of t h e Norwegian S e a , and he suggested t h a t only p a r t of t h e t o t a l O-group p o p u l a t i o n e n t e r e d t h e Norwegian f j o r d s . From l a t e r i n v e s t i g a t i o n s i t can b e s t a t e d t h a t t h e d i s t r i b u t i o n of t h e young and a d o l e s c e n t h e r r i n g i s widespread, ranging from t h e f j o r d s of n o r t h e r n

Fig. 2. D i s t r i b u t i o n of young h e r r i n g . ( l ) n u r s e r y a r e a , ( 2 ) l a r v a l d i s t r i b u t i o n ,

(3)

d i r e c t i o n of p o s t - l a r v a l d r i f t t o t h e o f f s h o r e n u r s e r y a r e a .

(9)

LIFE

HISTORY

-

h e r r i n g

...

A RECAPTURED

o" 5" 15"

Fig.

3.

D i s t r i b u t i o n of t a g r e t u r n s . A=

r e t u r n s from t h e w i n t e r f i s h e r y i n

1979,

B = r e t u r n s from t h e w i n t e r f i s h e r y i n

1989,

C= r e t u r n s from c a t c h e s taken i n t h e n o r t h e r n and s o u t h e r n w i n t e r i n g a r e a s of t h e h e r r i n g d u r i n g l a t e autumn.

(10)

L i f e h i s t o r y aiid e x p l o i t a t i o n

...

Norway t o t h e open ocean of t h e Norwegian Sea and t h e B a r e n t s Sea

(Dragesund and Hognestad, 1960; Devold, 1968; Jakobsson, 1968;

Dragesund, 1 9 7 0 ) . When r e c r u i t m e n t c o n d i t i o n s a r e f a v o u r a b l e , most of t h e j u v e n i l e h e r r i n g a r e found i n t h e B a r e n t s Sea ( R ~ t t i n g e n ,

1987).

F i g u r e 2 shows a schematic i l l u s t r a t i o n of t h e g e n e r a l d i s t r i b u t i o n of t h e e a r l y s t a g e s . Soon a f t e r h a t c h i n g , t h e l a r v a e rise i n t o t h e upper water l a y e r s and a r e t r a n s p o r t e d northwards from t h e spawning grounds.

During t h e northward d r i f t , p a r t of t h e l a r v a e accumulates a t t h e e n t r a n c e t o t h e f j o r d s a l o n g t h e Norwegian c o a s t . I n l a t e summer and e a r l y autumn O-group h e r r i n g a r e g e n e r a l l y recorded i n t h e t o p water l a y e r s a l o n g t h e Norwegian c o a s t and i n t h e B a r e n t s Sea (Dragesund, 1970; Anon., 1970). The o f f s h o r e d i s t r i b u t i o n i s , however, more v a r i a b l e and i s c l o s e l y r e l a t e d t o y e a r c l a s s s t r e n g t h , and hence t h e i n f l o w of A t l a n t i c water t o t h i s r e g i o n ( s e e s e c t i o n

5 ) .

I n l a t e autumn a major p a r t of t h e O-group i n o f f s h o r e waters i s c o n c e n t r a t e d along t h e f r o n t s between t h e c o l d a r c t i c water and t h e warmer water masses o f f t h e Spitsbergen-Bear I s l a n d and i n t h e c e n t r a l and s o u t h e a s t e r n p a r t s of t h e Barents Sea. The h e r r i n g remain i n t h i s a r e a d u r i n g t h e f o l l o w i n g w i n t e r and s p r i n g . During s p r i n g and e a r l y summer, t h e I-group h e r r i n g d i s t r i b u t e d i n t h e n o r t h e r n and n o r t h e a s t e r n p a r t of t h e Barents Sea move southwards. A t t h e same time, h e r r i n g of t h e same a g e , which have wintered i n t h e f j o r d s of n o r t h e r n Norway, m i g r a t e from t h e c o a s t and mix w i t h t h e open-sea c o n c e n t r a t i o n s . During t h e f o l l o w i n g w i n t e r t h e 2-group h e r r i n g a r e found i n almost t h e same a r e a , although t h e d i s t r i b u t i o n i s more r e s t r i c t e d t o c o a s t a l banks and t o t h e c e n t r a l and s o u t h e r n p a r t of t h e B a r e n t s Sea.

During summer and autumn p a r t of t h e 2-group h e r r i n g , t h e f a s t e s t growing f i s h , move westward i n t o t h e Norwegian Sea. However, most of t h e f i s h remain i n t h e B a r e n t s Sea and i n t h e a r e a o f f Finnmark f o r a n o t h e r y e a r b e f o r e they s t a r t t h e westward m i g r a t i o n i n t o t h e Norwegian Sea t o j o i n t h e a d u l t s t o c k . The s l o w e s t growing f i s h s t a r t t h e i r e m i g r a t i o n from t h e B a r e n t s Sea d u r i n g t h e 4-group s t a g e . The a d o l e s c e n t h e r r i n g moving i n t o t h e Norwegian Sea u s u a l l y have an o c e a n i c s t a g e b e f o r e they mature. Some i n d i v i d u a l s mature a f t e r one y e a r , o t h e r s a f t e r two o r t h r e e y e a r s (Dragesund e t . a l 1 9 8 0 ) .

This d i s t r i b u t i o n and m i g r a t i o n p a t t e r n of young and a d o l e s c e n t h e r r i n g i n t h e B a r e n t s Sea i s i n accordance with t h e o b s e r v a t i o n s of t h e movement of t h e

1983

y e a r c l a s s ( R ~ t t i n g e n ,

1989).

The c o a s t a l component of t h e

1983

y e a r c l a s s from t h e f j o r d s i n Finnmark mixed with t h e B a r e n t s Sea component i n

1984

and t h e mixed s t o c k l e f t t h e B a r e n t s Sea d u r i n g t h e s p r i n g and t h e summer 1986. Most o f t h e s e h e r r i n g had a one y e a r o c e a n i c s t a g e b e f o r e they matured and spawned f o r t h e f i r s t time i n

1988.

I n 1963-66 t h e 4-years o l d immature h e r r i n g wintered i n t h e Bear I s l a n d w i n t e r i n g a r e a , b u t most of t h e 1983 y e a r c l a s s wintered a s immature i n V e s t f j o r d e n a s

4

y e a r o l d s . RECRUITMENT AND AGE COMPOSITION

The age s t r u c t u r e of t h e a d u l t h e r r i n g s t o c k has been known s i n c e t h e beginning of t h i s c e n t u r y ( H j o r t , 1926)

.

I n a v i r g i n s t a t e , t h e l i f e span of h e r r i n g i s about 20-25 y e a r s . The m a t u r a t i o n of a y e a r c l a s s t a k e s p l a c e about some f i v e y e a r s , which means t h a t t h e a d u l t s t o c k may c o n s i s t of a s much a s 15-20 y e a r c l a s s e s . The r e c r u i t m e n t i s more- over v a r i a b l e and t h e s e f a c t o r s govern t h e age s t r u c t u r e of t h e s t o c k

(11)

LIFE HISTORY

-

h e r r i n g

L i f e h i s t o r y m-d e x p l o i t a t i o n

...

and t h e s t a b i l i t y of s t o c k abundance. The age composition of h e r r i n g from 1908 onwards compared with g e n e r a l i n f o r m a t i o n on s t o c k abundance i n d i c a t e t h a t t h e s t o c k recovered g r a d u a l l y a t t h e end o f t h e previous c e n t u r y . An e x t r a o r d i n a r y s t r o n g y e a r c l a s s was r e c r u i t e d i n 1904 which may have r e b u i l t t h e spawning s t o c k t o a l e v e l of

5

t o 10 m i l l i o n tonnes i n t h e second decade of t h i s c e n t u r y (Marty and Fedorov, 1963). Three r i c h y e a r c l a s s e s occured between 1900-1930, t h e y e a r c l a s s e s 1904,

1918

and 1923. The 1930's c o n s t i t u t e d a p e r i o d of good r e c r u i t m e n t and o n l y t h e y e a r c l a s s e s

1931

and 1936 were poor. I n t h e 1 9 4 0 ' s t h e r e were t h r e e r i c h y e a r c l a s s e s , t h o s e of

1943, 1944

and

1947

and a n o t h e r v e r y abundant y e a r c l a s s occurred i n 1950. According t o Marty and Fedorov t h e p e r i o d i c i t y of occurrence of abundant y e a r c l a s s e s ranged from one t o

14

y e a r s , whereas a seven y e a r s i n t e r v a l had been t y p i c a l from 1923 t o 1950. The a u t o r s a l s o showed t h a t t h e occurrence of abundant y e a r c l a s s e s c o i n s i d e d with i n c r e a s i n g i n f l o w o f warm water t o t h e B a r e n t s S e a , which a f f e c t s t h e mean Kola Meridian temperature. I n a r e c e n t paper S æ t e r s d a l and Loeng

(1984)

have shown t h a t a s i m i l a r c o r r e l a t i o n does e x i s t between t h e temperature of t h e Kola Meridian and r e c r u i t m e n t s u c c e s s f o r Northeast A r c t i c cod.

S i n c e 1950 abundant h e r r i n g y e a r c l a s s e s have o c c u r r e d i n 1959 and i960 c o i n s i d i n g with a warm c l i m a t e i n t h e Barents Sea. I n t h e e a r l y 7 0 t s , a n o t h e r warm p e r i o d occured, b u t a t t h a t time t h e spawning s t o c k of h e r r i n g was d e p l e t e d . I n r e l a t i o n t o spawning s t o c k t h e h e r r i n g y e a r c l a s s

1973

was known e x t r a - o r d i n a r y s t r o n g . The l a t e 1 9 7 0 ' s was a c o l d p e r i o d i n t h e B a r e n t s Sea. The c l i m a t i c c o n d i t i o n s improved i n t h e e a r l y 8 0 ' s and s t r o n g y e a r c l a s s e s were r e c r u i t e d i n t h e y e a r s 1983-85. The h e r r i n g y e a r c l a s s e s 1984-85 were however d e p l e t e d by i n c r e a s e d p r e d a t i o n from a very s t r o n g 1983 y e a r c l a s s of cod.

Recruitment a f t e r 1985 h a s been poor.

P l o t s of VPA-estimates of r e c r u i t m e n t v e r s u s spawning s t o c k biomass a r e shown i n F i g u r e 10 f o r t h e y e a r s 1950 onwards.The VPA f i g u r e s a r e d e r i v e d from t h e c a t c h i n number by y e a r c l a s s e s a d j u s t e d by a c o n s t a n t n a t u r a l m o r t a l i t y by age groups. V a r i a t i o n s i n t h e m o r t a l i t y due t o p r e d a t i o n o r o t h e r forms of s t o c k i n t e r a c t i o n s have n o t been accounted f o r . Judging from t h e s t o c k i n t e r r e l a t i o n s h i p observed i n r e c e n t y e a r s i t is assumed t h a t t h e s e r e c r u i t m e n t f i g u r e s a r e g r o s s l y u n d e r e s t i m a t e d , p a r t i c u l a r l y t h e r e c r u i t m e n t i n warm p e r i o d s when t h e cod have had f a v o u r a b l e r e c r u i t m e n t c o n d i t i o n s . The s t o c k - r e c r u i t m e n t p l o t demonstrates a l i n e a r r e l e a t i o n s h i p between s t o c k biomass and r e c r u i t m e n t when r e c r u i t m e n t c o n d i t i o n s a r e f a v o u r a b l e . When u s i n g c a t c h - r e l a t e d r e c r u i t m e n t f i g u r e s , t h i s a p p l i e s t o t h e f i r s t y e a r c l a s s which i s r e c r u i t e d i n a good r e c r u i t m e n t p e r i o d . The y e a r c l a s s e s of t h e subsequent y e a r s may however a l s o have been abundant a s O-group h e r r i n g , b u t may have been reduced a t a young age by p r e d a t i o n from abundant y e a r c l a s s e s of cod.

EXPLOITATION

The main f i s h e r y on a d u l t h e r r i n g has been t h e w i n t e r h e r r i n g f i s h e r y d u r i n g t h e spawning season. I n t h e p e r i o d 1925-1960 t h e w i n t e r h e r r i n g c a t c h e s were s h a r e d about e q u a l l y by p u r s e s e i n e r s and d r i f t e r s . E a r l i e r i n t h i s c e n t u r y t h e l a n d s e i n e was a l s o e x t e n s i v e l y used.

O r i g i n a l l y t h e p u r s e - s e i n e f i s h e r y was c a r r i e d o u t by v e s s e l s equipped with a p u r s e s e i n e o p e r a t e d from two d o r i e s . The r i n g - n e t technique w i t h power block r e p l a c e d t h e two-dory system i n t h e e a r l y 1 9 6 0 1 s , and most of t h e h e r r i n g h a s been caught by t h i s technique i n l a t e r y e a r s .

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...

Y E A R

F i g .

4 .

T o t a l c a t c h of a d u l t h e r r i n g 1925-1970.

The annua1 c a t c h e s from t h e a d u l t h e r r i n g f i s h e r y o v e r t h e p e r i o d 1925-1970 a r e shown i n F i g u r e

4.

D e t a i l s of t h e h e r r i n g c a t c h e s 1950-

1988

a r e given i n Table 1. Although t h e c a t c h e s f l u c t u a t e d c o n s i d e r a b l y , they d i d n o t show any major t r e n d up t o 1947. T h e r e a f t e r t h e c a t c h e s r o s e s t e a d i l y t o about one m i l l i o n tonnes i n 1954-1956, when t h e r i c h l950 y e a r c l a s s s t a r t e d t o r e c r u i t t o t h e spawning s t o c k . The c a t c h e s then f e l l s t e a d i l y , up t o 1963, t o a l e v e 1 n e a r t h a t of t h e p o o r e s t y e a r of t h e prewar p e r i o d . There was a recovery i n 1964 when t h e r i c h y e a r c l a s s e s of 1959 and 1960 e n t e r e d t h e s t o c k . From 1965 onwards a r a p i d d e c r e a s e i n t h e s t o c k s i z e took p l a c e , and t h e w i n t e r - h e r r i n g f i s h e r y c o l l a p s e d i n 1970.

The summer and autumn f i s h e r y on a d u l t s , took p l a c e on t h e f e e d i n g grounds a l o n g t h e P o l a r Front i n t h e Norwegian Sea. T h i s f i s h e r y was l o c a t e d f o r a l o n g p e r i o d o f f n o r t h e r n and n o r t h e a s t e r n I c e l a n d (Jakobsson, 1963). The f i s h i n g season normally l a s t e d from June t o e a r l y September, and up t o 1950 t h e s t o c k was mainly e x p l o i t e d by I c e l a n d i c and Norwegian v e s s e l s .

I n t h e e a r l y 19601s new t e c h n i c a l advances improved t h e technique i n t h e I c e l a n d i c f i s h e r y , a s they d i d i n t h e Norwegian h e r r i n g f i s h e r y , and t h e f i s h e r y extended seawards. During t h e 1 9 6 0 ' s t h e f i s h e r y took p l a c e f a r o f f s h o r e i n t h e Norwegian Sea, and t h e f i s h i n g season l a s t e d u n t i l October-November. I n 1966 when t h e r e c o r d c a t c h of a d u l t h e r r i n g was t a k e n , I c e l a n d caught 40% whereas Norway and USSR caught about

30%

of t h e t o t a l c a t c h each (Table 2 ) .

The S o v i e t d r i f t n e t f i s h e r y on f e e d i n g h e r r i n g i n t h e Norwegian Sea s t a r t e d i n 1950. I n i t i a l l y , t h e f i s h e r y was p u r e l y a summer o n e , e x p l o i t i n g t h e grounds between S p i t s b e r g e n , J a n Mayen, and I c e l a n d . I n

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LIFE HISTORY

-

h e r r i n g

...

1952 an autumn and w i n t e r f i s h e r y s t a r t e d along t h e migratory r o u t e s of t h e prespawning c o n c e n t r a t i o n s towards t h e spawning grounds o f f t h e Norwegian c o a s t .

The change i n t h e migratory p a t t e r n of t h e a d u l t s t o c k d u r i n g t h e 1 9 6 0 ' s s t r o n g l y i n f l u e n c e d t h e l o c a t i o n of t h e summer and autumn f i s h e r y . Off I c e l a n d i t became n e g l i g i b l e and most of t h e summer and autumn f i s h e r y i n t h e 1960's took p l a c e o f f t h e s h e l f s o u t h and, west o f Bear I s l a n d - S p i t s b e r g e n . From t h e 1 9 7 0 ' s onwards most of t h e h e r r i n g h a s been caught i n Norwegian c o a s t a l w a t e r s w i t h i n a range of some 20 n.m. o f f t h e c o a s t .

Y E A R

F i g .

5.

The c a t c h of young and a d o l e s c e n t h e r r i n g . ( 1 ) t h e t o t a l c a t c h , ( 2 ) t h e c a t c h of s m a l l h e r r i n g .

I n a d d i t i o n t o t h e f i s h e r y on a d u l t s , t h e young and a d o l e s c e n t h e r r i n g were f i s h e d a t t h e Norwegian c o a s t and i n t h e f j o r d s ( F i g u r e

5 ) .

Almost a l l t h e c a t c h e s were taken with p u r s e s e i n e , and from 1964 onwards t h e r i n g - n e t technique was used and t h e e f f i c i e n c y i n c r e a s e d . The most important s m a l l - h e r r i n g f i s h e r y o c c u r r e d i n t h e f j o r d s from l a t e autumn t o e a r l y s p r i n g .

STOCK ASSESSMENT

The abundance of t h e Norwegian s p r i n g spawning h e r r i n g s t o c k has been a s s e s s e d by v a r i o u s methods. Marty and Fedorov (1963) a s s e s s e d t h e s t o c k abundance and y e a r c l a s s s t r e n g t h f o r t h e p e r i o d 1904-1960 on t h e b a s i s of c a t c h by y e a r c l a s s e s i n s u c c e s i v e y e a r s a f t e r a method

developed by Denzhavin (1922). Dragesund and Jakobsson (1963)

e s t i m a t e d s t o c k s i z e and t o t a l m o r t a l i t y r a t e f o r t h e p e r i o d 1953-1960 on t h e b a s i s of t a g r e t u r n s from i n t e r n a l t a g g i n g experiments and Østvedt (1963) e s t i m a t e d t o t a l m o r t a l i t y from c a t c h and e f f o r t d a t a i n t h e d r i f t n e t f i s h e r y f o r t h e p e r i o d 1950-1960. The ICES Working Group on Atlanto-Scandian h e r r i n g ( h e r e a f t e r termed t h e Working Group), has i n two r e p o r t s (Anon. 1970, 1977) a s s e s s e d t h e s t a t e of t h e s t o c k f o r t h e p e r i o d

1953-1959,

u s i n g d a t a from v a r i o u s s o u r c e s . A conventional VPA f o r t h e y e a r s 1950-1971 i s p u b l i s h e d by Dragesund and U l l t a n g

(1978)

and t h e r e s u l t s of a somewhat a d j u s t e d v e r s i o n of t h i s a r e shown i n F i g u r e

7

(Dragesund e t . a l 1980)

.

The ICES Working Group r e s u l t s a r e i n c l u d e d f o r comparison. I n t h e p e r i o d

1975

onwards, t h e s t o c k h a s been a s s e s s e d by VPA, t a g g i n g and a c o u s t i c methods.

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...

Fig.

6.

( I ) Abundance i n d i c e s of some year c l a s s e s of Norwegian s p r i n g spawning h e r r i n g i n b i l l i o n s of f i s h , s t o c k values of h e r r i n g from t h r e e year o l d s and o l d e r , ( 2 ) mature h e r r i n g ,

(3)

by y e a r s i n m i l l i o n metric c e n t n e r s (Marty and Fedorov 1963).

Fig.

7.

Estimated spawning stock ( S ) , f i s h i n g m o r t a l i t y ( F ) and recruitment ( X ) of h e r r i n g 1950-1973 a s l year o l d . The

broken l i n e shows s t o c k e s t i m a t e s given by t h e Working Group.

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LIFE HISTORY

-

h e r r i n g

...

The s t o c k abundance e s t i m a t e s of h e r r i n g o l d e r t h a n

3

y e a r s f o r t h e p e r i o d 1904 t o 1960 a r e shown i n Figure 6 (Marty and Fedorov, 1963).

The n a t u r a l m o r t a l i t y h a s n o t been accounted f o r i n t h e s e e s t i m a t e s . According t o t h i s method, t h e accumulated c a t c h e s ranged between 1 . 5 and 2.0 m i l l . tonnes p r i o r t o 1925. Assuming t h a t t h e f i s h i n g m o r t a l i t y a t t h a t t i m e was lower than t h e n a t u r a l m o r t a l i t y , Marty and Fedorow found t h a t t h e s t a n d i n g s t o c k biomass must have been f i v e t o s i x t i m e s g r e a t e r t h a n t h e accumulated c a t c h f i g u r e s o r i n an o r d e r of magnitude of 10 m i l l . tonnes. For t h e 1 9 5 0 ' s t h e Dezhavin's method gave a s t o c k e s t i m a t e of 7 t o

8

m i l l . tonnes. Assuming t h a t t h e f i s h i n g m o r t a l i t y i n t h e 1 9 5 0 ' s was

5

times h i g h e r t h a n t h e n a t u r a l m o r t a l i t y t h e a u t h o r concluded t h a t t h e s t o c k may have remained on a s t e a d y s t a t e l e v e l of an o r d e r of magnitude of 1 0 m i l l . tonnes throughout t h e whole p e r i o d under s t u d y .

According t o t h e VPA ( F i g u r e 7 ) , t h e spawning s t o c k s i z e was a t a l e v e 1 of about 9 m i l l i o n tonnes i n l950 and decreased t o about 7 m i l l i o n tonnes i n 1953. From 1954 t o 1957 t h e s t r o n g 1950 y e a r c l a s s g r a d u a l l y r e c r u i t e d t o t h e spawning s t o c k , r e s u l t i n g i n an i n c r e a s e i n s t o c k s i z e t o about 10 m i l l i o n tonnes i n 1957. The s t o c k t h e n decreased t o about 2 . 5 m i l l i o n tonnes i n 1963 mainly a s a r e s u l t of poor r e c r u i t m e n t . From 1963 t o 1965 t h e spawning s t o c k s i z e i n c r e a s e d a g a i n , r e a c h i n g about

3.7

m i l l i o n tonnes i n

1965.

From 1966 onwards t h e r e was a r a p i d d e c r e a s e i n spawning s t o c k s i z e owing t o an almost complete l a c k of r e c r u i t m e n t t o t h e a d u l t s t o c k and r a p i d l y i n c r e a s i n g f i s h i n g m o r t a l i t i e s . The rise i n F d u r i n g t h e y e a r s 1963-1966 was caused by i n c r e a s i n g f i s h i n g e f f o r t , b u t t h e f u r t h e r l a r g e i n c r e a s e i n F i n 1967 onwards was probably mainly t h e e f f e c t of d e c r e a s i n g s t o c k s i z e caused by b o t h t h e i n c r e a s e i n f i s h i n g m o r t a l i t y i n previous y e a r s and t h e f a i l u r e i n r e c r u i t m e n t ( U l l t a n g 1 9 7 6 ) .

Y E A R - C L 4 S S 1

F i g .

8.

Year-class s t r e n g t h i n number a s O-group and

4

y e a r o l d s (broken l i n e ) , 1950-1969 (Dragesund e t a l . 1 9 8 0 ) .

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...

Comparing t h e p r e s e n t e s t i m a t e s of s t o c k s i z e and r a t e of e x p l o i t a t i o n of a d u l t s from VPA with e a r l i e r Working Group e s t i m a t e s , i t can be concluded t h a t t h e Working Group assessed t h e s i t u a t i o n more o r less c o r r e c t l y u n t i l t h e r a p i d i n c r e a s e i n f i s h i n g e f f o r t s t a r t e d i n t h e e a r l y 1 9 6 0 1 s , i . e . b e f o r e t h e i n t r o d u c t i o n o f t h e r i n g - n e t technique.

T h e r e a f t e r t h e Working Group badly overestimated t h e s t o c k s i z e .

The e x p l o i t a t i o n r a t e of young h e r r i n g was a l s o high d u r i n g t h e p e r i o d 1950-1969. I n F i g u r e

8

a r e given t h e VPA e s t i m a t e s of y e a r c l a s s s t r e n g t h a s O and

4

y e a r s o l d i n t h e p e r i o d . The F i g u r e shows t h a t y e a r c l a s s e s i n t h e 1 9 5 0 ' s which have t r a d i t i o n a l l y been d e s c r i b e d a s weak, were a l l of what could be c a l l e d normal s t r e n g t h 1 0 * 1 0 ~ t o 3 0 . 1 0 ~ f i s h a t t h e O-group s t a g e . However, y e a r c l a s s of s t r e n g t h s l e s s t h a n 20.

lo9

a s O-group s u r v i v e d t h e f i s h e r y o n l y i n s m a l l q u a n t i t i e s t o reach t h e age of

4

y e a r s . The 1965 y e a r c l a s s w a s t h e f i r s t one i n t h e p e r i o d s t u d i e d which r e a l l y should be c l a s s i f i e d a s weak a t t h e O-group s t a g e (Dragesund and U l l t a n g ,

1978).

The VPA c l e a r l y shows t h a t t h e f i s h i n g p r e s s u r e , on young and a d o l e s c e n t h e r r i n g i n g e n e r a l and on a d u l t h e r r i n g i n t h e y e a r s 1965- 1968, was t h e primary f a c t o r i n t h e c o l l a p s e of t h i s h e r r i n g s t o c k . A s mentioned p r e v i o u s l y some few h e r r i n g of t h e 1969 y e a r c l a s s s u r v i v e d a s j u v e n i l e s i n t h e e a r l y 1 9 7 0 ' s i n t h e Barents Sea and some v e r y few s u r v i v e d on t h e More c o a s t . These s t o c k components have i n l a t e r y e a r s been a s s e s s e d by an a c o u s t i c method and by t a g g i n g a s a d u l t s . An echo abundance survey of O-group h e r r i n g i n t h e Norwegian f j o r d s were i n i t i a t e d i n

1975

and extended t o cover t h e d i s t r i b u t i o n a r e a of O-group h e r r i n g i n t h e Barents Sea s i n c e

1983.

The survey a r e c a r r i e d o u t i n November-December and t h e technique used i s t h e same a s t h a t a p p l i e d f o r c a p e l i n (Nakken and Dommasnes

1975).

The r e s u l t s appear from t h e t e x t t a b l e below:

C o a s t a l B a r e n t s

Year comp

.

^Sea

1975

1 . 0

1976

3.8 1977 o. 4 l978

1 . 2

1979

3.4

1980 0.2

1981

O. 2

1982 2.9

1983

13.7

35.7 1984 1 . 4

6 . 2

1985

1 . 0

41.5

1986 0.4 O

1987

0 . 3 O

1988

2 . 5 9

8

These r e c r u i t m e n t f i g u r e s a r e n o t comparable t o t h e back c a l c u l a t e d r e c r u i t m e n t number of l-group h e r r i n g ( R 1 ) d e r i v e d from t h e VPA. I n t h e s t o c k p r o g n o s i s t h e a c o u s t i c O-group e s t i m a t e s have been used a s i n d i c e s of r e c r u i t m e n t a t age

3

by s c a l i n g t h e number down by a c a l c u l a t e d conversion f a c t o r of 0.51 (Anon. 1986).

Compared t o t h e p e r i o d b e f o r e t h e s t o c k c o l l a p s e i n t h e l a t e 1 9 6 0 ' s t h e r e c r u i t m e n t i n l a t e r y e a r s h a s been extremely low e x c e p t f o r t h e

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LIFE HISTORY

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h e r r i n g

...

y e a r s

1983-85.

The s t o c k h a s been g r o s s l y r e c r u i t m e n t o v e r e x p l o i t e d , b u t i n t h e y e a r s 1975-82 t h e r a t e o f r e c r u i t m e n t h a s a l s o been low.

T h i s was probably due t o unfavourable r e c r u i t m e n t c o n d i t i o n , l i n k e d t o low water temperatures i n t h e Barents Sea (Marty and Fedorov 1963, H a m r e

1988).

Assessment by tagging

I n t h e p e r i o d 1975-1986 t h e s t a t e of t h e a d u l t s t o c k has been a s s e s s e d by t u n i n g t h e VPA a g a i n s t s t o c k estimates o b t a i n e d from t a g g i n g (Anon.

1980,1986). The tagging p r o j e c t a s w e l l a s t h e model used f o r t h e p r o c e s s i n g of t h e d a t a have been d e s c r i b e d i n working documents and r e p o r t s of t h e Working Group (Anon. 1984,1986).

The t a g g i n g p r o j e c t u s i n g i n t e r n a l s t e e l t a g s was i n i t i a t e d i n 1975 and s i n c e then h e r r i n g have been tagged and r e l e a s e d a n n u a l l y on v a r i o u s l o c a l i t i e s along t h e w e s t c o a s t i n April-May. P r i o r t o 1982 t h e h e r r i n g were caught by p u r s e s e i n e , towed t o t h e s h o r e and k e p t i n keepnets b e f o r e tagging. S i n c e 1982 t h e h e r r i n g have been b r a i l e d from t h e s e i n e t o t h e RSV-tanks onboard t h e s e i n e r and tagged and r e l e a s e d from t h e t a n k s . The tagged h e r r i n g a r e r e l e a s e d i n b a t c h e s and under v a r i o u s c o n d i t i o n s and t h e m o r t a l i t y due t o t h e t a g g i n g i s expected t o be v a r i a b l e .

The tagged h e r r i n g a r e recovered by s c r e e n i n g h e r r i n g c a t c h e s u s i n g a s p e c i a l c o n s t r u c t e d i n t e r n a l t a g d e t e c t o r . The e f f i c i e n c y of t h e d e t e c t o r i s t e s t e d by mixing tagged h e r r i n g w i t h t h e c a t c h b e f o r e s c r e e n i n g (Gytre and Jakupsstovu, 1977).

The r e c o v e r i e s used f o r s t o c k assessment a r e a l l o b t a i n e d from w i n t e r c a t c h e s o f spawners and prespawners. The commercial h e r r i n g w i n t e r f i s h e r y was p r o h i b i t e d u n t i l 1984, b u t experimental f i s h i n g f o r t a g recovery was allowed d u r i n g t h e w i n t e r s 1977-83. The commercial w i n t e r f i s h e r y was opened i n

1984

and i n later y e a r s both commercial and experimental c a t c h e s have been screened f o r t a g s . The h e r r i n g s t o c k h a s developed i n two s e p a r a t e u n i t s , and t h e d a t a on r e l e a s e s and corresponding r e c o v e r i e s a r e prosessed by t h e two s t o c k components s e p a r a t e l y . The tagging i s done d u r i n g t h e f e e d i n g s e a s o n , and i n a r e a s where s h o a l s from both components a r e d i s t r i b u t e d . It has t h e r e f o r e been d i f f i c u l t t o a l l o c a t e t h e r e l e a s e s on components when r e l e a s e d . The tagged h e r r i n g a r e r e l e a s e d i n b a t c h e s of 2 000

-

10 000 i n d i v i d u a l s , and t h e a l l o c a t i o n of t h e batches on components i s made on t h e b a s i s of t h e r e c o v e r i e s , i . e . , t h e p o s i t i o n and t h e age- composition of t h e c a t c h e s from which t h e bulk o f t h e r e c o v e r i e s a r e r e t a i n e d . The b o ~ n d a r y ~ b e t w e e n t h e spawning grounds of t h e two compo- n e n t s runs a t about 63 N.

By t h i s grouping of d a t a t h e c o n s i s t e n c y of t h e abundance e s t i m a t e s by y e a r s i s improved, b u t t h e r e s u l t s i n d i c a t e t h a t no random mixing of t h e tagged f i s h i n t h e two s t o c k u n i t s i s a major source of e r r o r i n t h e e s t i m a t e s . The r e l e a s e s and r e c o v e r i e s by components and y e a r s a r e given i n Table

3 .

A t t h e bottom of t h e t a b l e i s given t h e corresponding number of h e r r i n g e f f e c t i v e l y screened f o r t a g s .

M o r t a l i t y estimates

The most simple model f o r e x p l i c i t e s t i m a t e s of s u r v i v a l r a t e from two s u c c e s s i v e r e l e a s e s i s t h e R i c k e r ' s model (Ricker 1975):

(18)

LIFE HISTORY

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h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n , . .

where Sl = s u r v i v a l r a t e d u r i n g y e a r 1

Ml ⁼ number marked a t t h e s t a r t of t h e first y e a r M2 ⁼ number marked a t t h e s t a r t of t h e second y e a r R l l = r e c a p t u r e s of f i r s t - y e a r marked i n t h e f i r s t

y e a r

R12 = r e c a p t u r e s of f i r s t - y e a r marked i n t h e second y e a r

R 2 * = r e c a p t u r e s of second y e a r marked i n t h e second y e a r

I f sampling i s done over a s e r i e s of y e a r s , t h e r e c a p t u r e s can b e summarized over t h e whole p e r i o d . A review of models f o r e x p l i c i t e maximum-likelihood e s t i m a t e s of animal abundance by t a g g i n g is published by Seber (1982). These methods presuppose t h a t t h e t a g g i n g m o r t a l i t y i s n e g l i g i b l e o r a t l e a s t does n o t v a r y with r e l e a s e s . T h i s u n d e r l y i n g assumption i s n o t f u l f i l l e d i n t h e p r e s e n t experiment, and a r e g r e s s i o n model h a s t h e r e f o r e been a p p l i e d .

The r e g r e s s i o n model e s t i m a t e s t h e t o t a l i n s t a n t a n e o u s m o r t a l i t y r a t e Z f o r e q u a l time p e r i o d s when Z i s assumed t o be c o n s t a n t . Two t y p e s of models a r e a v a i l a b l e . It can be shown t h a t i f t h e r e t u r n s from one r e l e a s e over a l o n g t i m e serie a r e grouped i n e q u a l t i m e i n t e r v a l s , t h e logarithm t o t h e number of r e t u r n s from each of t h e t i m e i n t e r v a l s p l o t t e d a g a i n s t t i m e , w i l l y i e l d a s t r a i g h t l i n e w i t h s l o p e e q u a l t o t h e i n s t a n t a n e o u s m o r t a l i t y r a t e (Gulland

1973).

It i s noted t h a t t h e m o r t a l i t y e s t i m a t e from t h i s model is independent of t h e number r e l e a s e d and consequently a l s 0 of t h e m o r t a l i t y due t o t h e tagging.

I n an analogous way i t can be proved t h a t i f Z i s c o n s t a n t t h e logarithm t o t h e f r a c t i o n number released/number recovered from s u c c e s s i v e r e l e a s e s i n t h e same c a t c h p l o t t e d a g a i n s t time i n l i b e r t y w i l l y i e l d

a s t r a i g h t l i n e with s l o p e e q u a l t o t h e i n s t a n t a n e o u s m o r t a l i t y Z. I f t h e s u r v i v a l s of t h e l a s t r e l e a s e a r e denoted so mo t h e s t o c k s i z e N according t o a P e t e r s e n e s t i m a t e is:

o

where s i s t h e c o e f f i c i e n t of s u r v i v a l a f t e r t a g g i n g and r i s t h e

o o

number of r e c o v e r i e s i n t h e c a t c h C o .

An e s t i m a t e of No may a l s a be expressed by t h e r e c o v e r i e s from t h e p r e v i o u s y e a r s ' r e l e a s e s a s follows: